As semiconductor devices, for example, display devices which display an image are known. In an active-matrix display device, thin-film transistors (TFTs) are employed for the switching elements of pixels. Further, the thin-film transistors are provided in a non-display area (peripheral area) outside a display area (active area). The thin-film transistors provided in the non-display area include diode-connected thin-film transistors.
For example, the diode-connected thin-film transistors are connected to lines extending in the display area, and function as protective diodes which protect the switching elements of pixels from static electricity. Thus, when voltage greater than or equal to a certain level is applied to the lines of the display area, the protective diodes are configured to supply current.